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As this trip around Sol comes to a close, the annual tradition of creating "best of the year" lists is in full swing. Here, we cover Science magazine's top scientific breakthroughs of 2007. As one can see at a quick glance, a diverse set of scientific fields are represented, from genetics to neuroscience to computer science. We'll start out with the breakthrough that earned top honors, then continue onto the nine runners-up, in no particular order.

Science's Breakthrough of the Year: human genetic variation

Nearly seven years ago, the human genome was first sequenced. Since then, continued rapid advancement in the field of genomics has allowed us to look even closer at ourselves to see what makes us, well, us. From studying our genetic makeup, scientists have found that there are about 15 million places along the genome where a person or population can differ. By the end of 2007, more than 3 million of these single-nucleotide polymorphisms (SNPs) were identified. An international scientific undertaking known as the HapMap Project is seeking to quantify the differences within the human genome by tracking these SNPs.

Using the catalog created by the HapMap Project, scientists are able to carry out genome-wide association studies. In doing so, they can look at hundreds of thousands of SNPs in a large number of people, then cross reference the distribution of SNPs with various symptoms that test subjects report. By examining any correlations that come out of such an statistical analysis, researchers can associate a risk of symptom with a single SNP (or a set of them).

In the past year alone, researchers linked more then a dozen diseases to fifty genes and their variants. While the link is often minimal, and a mechanism is not immediately known, the sheer number of people involved in the studies make the statistics hard to ignore. Studies published this year have found gene variants that hint at a predisposition for type 1 and 2 diabetes, Crohn's disease, heart disease, breast cancer, restless leg syndrome, atrial fibrillation, glaucoma, multiple sclerosis, rheumatoid arthritis, and colorectal cancer, among others.

In addition to the basic scientific breakthroughs that have made these discoveries possible, this field of work has opened up an entire new avenue of business: personal genomics. A host of companies have sprung up to offer a glimpse into one's personal genome and all the risk factors it may contain. Depending on how much money you are willing to spend, you can receive a quick once-over of your genome—for a mere $1,000-$2,500—or a complete sequencing of the entire thing that costs upwards of $1 million.

As usual, technology is outpacing ethics. Many feel that the information gained from these tests could be used against a person. An insurance company refusing coverage due to a known risk is the canonical example. A separate concern comes from the personal side: if a person finds out they have a predisposition to an incurable disease, even if it is still a very slight risk, the person may worry needlessly. Regardless of how this arena of business turns out, the gigantic leaps forward in genomic technology has earned Science magazine's Breakthrough of the Year award for 2007.

Runners-Up:

Stem Cells from Skin Cells: Last year, scientists in Japan created induced pluripotent stem (iPS) cells by inserting a mere four genes into mouse tail cells. These iPS cells looked and acted like embryonic stem cells. Over the summer a series of papers demonstrated how one could use mice skin cells to form these iPS cells. Then, in a shockingly fast sequence of events, not one but two research teams reported accomplishing the same feat with human skin cells. This is hailed as a victory by many scientists and politicians, as it potentially removes the need for use of human embryos in stem cell research.

Origin of Cosmic Bullets: It has been known since the 1960s that the Earth is bombarded by high energy cosmic particles. These particles are smaller than atoms yet hit the Earth with the force of a golf ball landing on a fairway—that is an energy level 100 million times higher then any particle accelerator has been able to achieve to date. The question of their origin may have been solved this year by researchers at the Pierre Auger Observatory in Argentina. Their answer: these particles come from active galactic nuclei, supermassive black holes at the center of some galaxies. However, without a mechanism to explain how these particles, protons in this case, reach these incredible energies (in excess of 60 EeV), the debate rages on.

Seeing Your Senses: While everyone knows the five basic senses, a detailed molecular understanding of how they work has yet to be elucidated. This year a pair of crystallographers published a set of four papers in Science, Nature, and Nature Methods reporting on the structure of the β2-adrenergic receptor. This molecule is one of a family of nearly 1,000 membrane-spanning molecules called G protein-coupled receptors (GPCRs). GPCRs help clue us into our surroundings through taste, smell, touch, hearing, and sight, and they help manage our internal body conditions.

Transition Metal Oxides: Diodes and transistors are the building blocks of the modern digital age. They owe their existence to the fact that when two semiconducting materials are put next to each other, all sorts of interesting physics result. This year material scientists found that if different transition metal oxides are grown in layers, very interesting things can occur. At a sharp interface between two types of oxides, the effect of the various crystal structures can change the positions of atoms along the interface, or even affect the electron charge distribution around certain atoms. In a pair of examples, researchers grew together two insulating materials that made a conducting interface, and another researcher created a superconducting interface from two insulators.

Quantum Spin Hall Effect: When theorists and experimentalists team up in science, breakthroughs happen. This year, a team of theoretical physicists predicted that mercury telluride (HgTe) sandwiched between two semiconducting materials should exhibit what is known as the quantum spin Hall effect (QSHE). When they began working with a group of experimental physicists, the combined team started down the path of proving this assertion. The quantum spin Hall effect was demonstrated, but only at temperatures below 10 K. If this can be reproduced at room temperatures, the effect could lead to a new generation of low-power "spintronic" computing devices.

Specialized Immune Cells: When you get sick, two types of immune cells are created. Some of the cells become "short-lived soldiers" whose job it is to fight off the disease. Other cells become long term memory cells that hang around for years or decades in case the same disease is encountered again. In March, a team of American researchers showed that a T cell could divide in an asymmetric manner that would allow for specialization as soldiers or memory cells. While no practical applications have yet come from this, it holds the potential to give vaccines a further kick.

Molecular Control: No specific breakthrough is cited here. Instead the mention is shared by chemists around the world for various breakthroughs in control over chemical reactions. When making a commodity chemical, the less steps it takes, the better. As any chemical engineer will tell you, separations and purifications between steps are expensive, and the cost of extra steps is passed on to the consumer. This year saw a flurry of advanced chemistry research that allows chemists to carry out reactions at selected sites on complex molecules, and thus has cut multiple steps in very long synthesis chains. In the end, this can potentially result in cheaper materials and pharmaceuticals for consumers.

Memory and Imagination: Neuroscience researchers this year found that there is a similarity between how our brain recollects memories and imagines new scenarios. In January, UK researchers showed that patients with amnesia—caused by damage to the hippocampus—had a difficult time imagining hypothetical situations as well as recalling old memories. Later in the spring, a separate brain imaging study of healthy young adults showed that similar neural pathways were used to both recall past events and imagine future scenarios—both used a part of the hippocampus.

Perfect Checkers: A team of Canadian computer science researchers proved that a game of checkers, if played perfectly, will end in a draw—no matter what. This proof is the culmination of 18 years of research and represents "the most complicated game ever 'solved'." In a game of US checkers, there around 5x1020 possible different configurations. Drawing from a database of 39 trillion possible arrangements of 10 or fewer pieces on the board, the researchers found which would lead to a win for red, a win for black, or a draw. They then demonstrated that a specific opening sequence, played perfectly, would invariably lead to a configuration that ended in a draw.

So that's what Science thinks were the biggest breakthroughs of the year. Readers should keep an eye out for Nobel Intent's take on the biggest science stories of the year in the upcoming week. To see how these breakthroughs compare to those from last year, feel free to check out Ars Technica's coverage from a year ago.

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Matt Ford
Matt is a contributing writer at Ars Technica, focusing on physics, astronomy, chemistry, mathematics, and engineering. When he's not writing, he works on realtime models of large-scale engineering systems. Emailzeotherm@gmail.com//Twitter@zeotherm